I can't find the photo with a quick google, but way back in the day an employee posted a photo of a TON of G5s arriving at Microsoft HQ.. supposedly they got fired for it, and it wasn't until a year or two later when the 360 was announced that everyone put two and two together.

Hundreds of comments, apparently this news went around the world. I assume they thought at the time the Macs were needed for developing MS Office for Mac OS.

Just for anybody that’s interested, here’s a ton of information about the G5 dev kits for the Xbox 360.

https://www.xenonwiki.com/Alpha

Yeah, the poor guy didn't know anything about Xbox, just thought it was funny that Microsoft was receiving so many G5 Macs:

https://www.smh.com.au/technology/microsoft-fires-employee-f...

Fun fact: The PowerMac G5 CPU cooling fan controllers have a failsafe mode: If the OS doesn't communicate with the fan controller, the fan controller assumes the worst: that the CPU is switched into the most power-hungry mode possible. To prevent potential damage to the CPU, after about 30 seconds, the cooling fans are cranked up to extraordinarily loud levels.

Apple didn't document how to control the fans. It took Microsoft a while to reverse-engineer the fan controllers. During that time period, using the G5s as Xbox dev kits required putting up with extraordinarily loud fans.